Field of the Invention
The present invention relates to a fuel cell separator and a manufacturing method of a fuel cell separator.
Description of Related Art
A technique has been developed of using titanium which is highly resistant to corrosion as a base substrate of a fuel cell separator and coating the titanium base substrate with a carbon thin film (carbon film). In this technique, ensuring adhesion between the titanium base substrate and the carbon film is a particularly important issue.
Usually, a surface layer of a titanium member is covered with a naturally-occurring oxide layer, which is a TiO2 layer. Since a TiO2 layer itself is a stable and dense layer, it serves as a protective film providing good corrosion resistance. However, when forming a carbon film on the titanium member, such TiO2 layer may be a factor leading to deterioration of adhesion.
Conventionally, various techniques have been adopted to improve the adhesion between the titanium member and the carbon film. For example, a known method removes the TiO2 layer in a vacuum by means of etching, and another known method forms an intermediate layer of TiC, etc., in advance (see, for example, JP4825894 B). In the method of removing the TiO2 layer by etching, when the carbon film is formed after the TiO2 layer is completely removed, a compound of Ti and C, i.e., TiC or TiCx, is formed on the interface between the titanium member and the carbon film, and such TiC or TiCx serves as an adhesion layer (binder layer). In other words, fuel cell separators formed by such conventional methods have a Ti/TiC/C structure.